This invention relates generally to wood filled plastic building members especially for use as a wood replacement in exterior structural applications and to the method of making such members.
Wood is widely used for structural members in both interior and exterior building applications. One of the objections to using wood for exterior applications is its high maintenance cost. Also, if not properly maintained and left exposed to harsh environments, wood will eventually rot or decay and have to be replaced.
It is generally known to make rot resistant window and door components and other structural members out of wood filled plastic compounds. Also, it is generally known that such wood filled plastic compounds can be extruded. However, hollow wood filled plastic extrusions are not very stiff and do not have good fastener hold strength, making them unsuitable for many structural member applications.
The present invention provides a cost effective way of commercially producing rigid wood filled plastic building members having good fastener holding capabilities.
In accordance with one aspect of the invention, a hollow elongated member of the desired general size and external shape or profile is extruded out of a suitable wood filled plastic compound and subsequently filled with a rigid plastic foam material.
In accordance with another aspect of the invention, during the extrusion process, the exterior profile of the member is intentionally extruded oversize and subsequently finished to the desired tolerance after the extruded member has been filled with rigid plastic foam.
In accordance with another aspect of the invention, the wood filled thermoplastic compound from which the member is extruded is comprised of between 50 to 80% thermoplastic and 50 to 20% wood fill with approximately 65% polystyrene and 35% wood flour being preferred.
In accordance with another aspect of the invention, the foam material used to fill the extruded wood filled plastic member is preferably a rigid high density, low pressure polyurethane foam.
In accordance with another aspect of the invention, after the hollow extruded member is filled with rigid plastic foam and finished to the desired tolerance, a prime coat of acrylic latex based paint is preferably applied to the exterior profile of the member.
These and other aspects, objects, advantages and features of the present invention will become apparent as the following description proceeds.
To the accomplishment of the foregoing and related ends, the invention, then, comprises the features hereinafter fully described and particularly pointed out in the claims, the following description and the annexed drawing setting forth in detail a certain illustrative embodiment of the invention, this being indicative, however, of but one of the various ways in which the principles of the invention may be employed.